Tunnel crews lowering groundwater to get a closer look at what’s blocking Bertha

Posted on Dec 13 2013 4:33 PM

Seattle Tunnel Partners (STP), our design-build contractor for the tunnel project, has taken their first step toward identifying and removing the potential obstruction that last week stopped the progress of Bertha, the SR 99 tunneling machine. STP is installing up to 10 wells approximately 120 feet deep on the construction site near the machine, which is located about 60 feet below the surface between South Jackson and South Main streets, to the west of the Alaskan Way Viaduct.

The wells will lower the water pressure in the ground to create a safe environment for workers to enter the excavation chamber at the front of the machine, where they'll be better able to assess the situation. High groundwater pressure combined with loose soils has to this point prevented safe worker access. Well installation started on Thursday and will continue into next week. STP hopes to begin inspecting the machine by late next week. 

To date, crews have successfully installed more than 1,000 feet of tunnel. Work continues inside the tunnel as well as in the north and south portals.

Previous updates

Dec. 5, 2013 update -- Seattle Tunnel Partners: Almost the proud owners of the world's largest tunneling machine

Nov. 25, 2013 update -- Bertha has much to be thankful for as she nears South Jackson Street

Nov. 14, 2013 -- Bertha takes on the complexities of King Street

Nov. 7, 2013 -- Several days at the dentist: new teeth will give Bertha more bite

Oct. 30, 2013 -- Bertha begins her week of scheduled maintenance